1. Field of the Invention
<First Technical Field>
The first technical feature disclosed in the present specification relates to a technique for increasing the slew rate of an operational amplifier.
<Second Technical Field>
The second technical feature disclosed in the present specification relates to a parameter setting and generating circuit, and a semiconductor device and a power supply unit incorporating the parameter setting and generating circuit.
2. Description of Related Art
<First Technical Background>
FIG. 5 is a schematic view showing a conventional example of an operational amplifier. In the conventional operational amplifier, a sudden change in a positive-phase input signal impressed on a positive-phase input terminal INP causes the operational amplifier to attempt to output an output signal that follows the input variation. The operational amplifier is required to deliver a rapid response performance (slew rate) during this process. Conventionally, it has been necessary to make the drive current Id of the operational amplifier more powerful and to drive the gate of the metal oxide semiconductor (MOS) field effect transistor that forms the output part of the operational amplifier at a higher rate in order to increase the slew rate of the operational amplifier.
Japanese Laid-open Patent Application No. 8-56128 can be given as one example of the prior art with relation to the above.
<Second Technical Background>
FIG. 10 is a circuit diagram showing a conventional example of an overcurrent protection circuit. The conventional overcurrent protection circuit shown in FIG. 10 is configured so as to be built into a semiconductor device 300 (DC/DC controller IC) that functions as part of a step-down switching regulator operating in synchronous rectification mode, to compare a predetermined threshold voltage Vth and a pulsed switch voltage Vsw (more accurately, a second switch voltage Vsw2 obtained by extracting only a low-level electric potential of the switch voltage Vsw obtained during the on-state of the transistor N2) brought out from the drain of an external transistor N2 mounted on the semiconductor device 300, and to generate an overcurrent protection signal OCP.
Japanese Laid-open Patent Application No. 2008-187847 filed by the present applicant can be given as one example of the prior art with relation to the above.